1. Field of the Invention
This invention is concerned with the demetalation and desulfurization of oil. More particularly, this invention relates to the use of a regenerable catalyst of controlled pore size distribution for demetalation and desulfurization of oil.
2. Description of the Prior Art
Residual petroleum oil fractions produced by atmospheric or vacuum distillation of crude petroleum are characterized by relatively high metals and sulfur content. This comes about because practically all of the metals present in the original crude remain in the residual fraction, and a disproportionate amount of sulfur in the original crude oil also remains in that fraction. Principal metal contaminants are nickel and vanadium, with iron and small amounts of copper also sometimes present. Additionally, trace amounts of zinc and sodium are found in some feedstocks. The high metals content of the residual fractions generally precludes their effective use as charge stocks for subsequent catalytic processing such as catalytic cracking and hydrocracking. This is so because the metal contaminants deposit on the special catalysts for these processes and cause the premature aging of the catalyst and/or formation of inordinate amounts of coke, dry gas and hydrogen.
It is current practice to upgrade certain residual fractions by a pyrolitic operation known as coking. In this operation, the residuum is destructively distilled to produce distillates of low metals content and leave behind a solid coke fraction that contains most of the metals. Coking is typically carried out in a reactor or drum operated at about 800.degree. to 1100.degree. F. temperature and a pressure of 1 to 10 atmospheres. The economic value of the coke by-product is determined by its quality, especially its sulfur and metals content. Excessively high levels of these contaminants make the coke useful only as low-valued fuel. In contrast, cokes of low metals content, for example up to about 100 p.p.m. (parts per million) by weight of nickel and vanadium, and containing less than about 2 weight percent sulfur, may be used in high-valued metallurgical, electrical and mechanical applications.
Certain residual fractions are currently subjected to visbreaking, which is a heat treatment of milder conditions than used in coking, in order to reduce their viscosity and make them more suitable as fuels. Again, excessive sulfur content sometimes limits the value of the product.
Residual fractions are sometimes used directly as fuels. For this use, a high sulfur content in many cases is unacceptable for ecological reasons.
At present, catalytic cracking generally utilizes hydrocarbon charge stocks lighter than residual fractions, which generally have an API gravity less than 20. Typical cracking charge stocks are coker and/or crude unit gas oils, vacuum tower overhead, etc., the feedstock having an API gravity from about 15 to about 45. Since these cracking charge stocks are distillates, they do not contain significant proportions of the large molecules in which the metals are concentrated. Such cracking is commonly carried out in a reactor operated at a temperature of about 800.degree. to 1500.degree. F., a pressure of about 1 to 5 atmospheres absolute, and a space velocity of about 1 to 1000 WHSV.
The amount of metals present in a given hydrocarbon stream is often expressed as a charge stock's "metals factor". This factor (F.sub.m) is equal to the sum of the metals concentrations, in parts per million, of iron and vanadium plus ten times the concentration of nickel and copper in parts per million, and is expressed in equation form as follows: EQU F.sub.m =Fe+V+10 (Ni+Cu)
Conventionally, a charge stock having a metals factor of 2.5 or less is considered particularly suitable for catalytic cracking. Nonetheless, streams with a metals factor of 2.5 to 25, or even 2.5 to 50, may be used to blend with or as all of the feedstock to a catalytic cracker, since charge stocks with metals factors greater than 2.5 in some circumstances may be used to advantage, for instance with the newer fluid cracking techniques.
In any case, the residual fractions of typical crudes will require treatment to reduce the metals factor. As an example, a typical Kuwait crude, considered of average metals content, has a metals factor of about 75 to about 100. As almost all of the metals are combined with the residual fraction of a crude stock, it is clear that at least about 80% of the metals and preferably at least 90% must be removed to produce fractions (having a metals factor of about 2.5 to 50) suitable for cracking charge stocks.
Metals and sulfur contaminants would present similar problems with regard to hydrocracking operations which are typically carried out on charge stocks even lighter than those charged to a cracking unit. Typical hydrocracking reactor conditions consist of a temperature of 400.degree. to 1000.degree. F. and a pressure of 100 to 3500 p.s.i.g.
It is evident that there is considerable need for an efficient method to reduce the metals and/or sulfur content of petroleum oils, and particularly of residual fractions of these oils. While the technology to accomplish this for distillate fractions has been advanced considerably, attempts to apply this technology to residual fractions generally fail due to very rapid deactivation of the catalyst, presumably by metal contaminants.
By the 1960's, there was universal recognition in the art that hydrogenation catalysts comprising Group VI and Group VIII metals of their oxides or sulfides deposited on porous refractory supports were extremely useful in the demetalation and desulfurization of residue hydrocarbon fractions. Particularly preferred catalysts were considered to be cobalt-molybdate or nickel-cobalt-molybdate supported on alumina. These catalysts are generally referred to as "conventional HDT catalysts" or "conventional hydrotreating catalysts".
The pore size distribution of the catalyst utilized for demetalation and/or desulfurization is a very important parameter. Large pore catalysts generally possess greater demetalation activity than smaller pore catalysts; small pore catalysts generally possess higher desulfurization activity than large pore catalysts. Processes utilizing pore size distribution can be considered to fall into one of the following categories: (1) the use of a single catalyst pore size distribution for demetalation; (2) the use of a single catalyst pore size distribution for desulfurization; (3) the use of a single catalyst pore size distribution for both demetalation and desulfurization; and (4) the use of two or more catalysts with different pore size distributions, where one or more catalysts are generally for demetalation and other catalysts are generally for desulfurization.
U.S. Pat. Nos. 3,393,148; 3,674,680; 3,764,565; 3,841,995 and 3,882,049 disclose desulfurization processes using an average pore diameter size for conventional HDT catalysts of 100 to 200 Angstroms.
There are many processes geared to the hydrodesulfurization of residual oil fractions utilizing conventional HDT catalysts characterized by a specific pore size distribution. Examples of such processes are described in U.S. Pat. Nos. 3,730,879; 3,814,683; 3,902,991; 4,032,435; 4,051,021; 4,069,139 and 4,073,718.
Processes for the demetalation and desulfurization of residual oil fractions employing conventional HDT catalysts characterized by having at least 60% of their pore volume in pores having diameters of 100 to 200 Angstroms and at least 5% of their pore volume in pores having diameters greater than 500 Angstroms are disclosed in U.S. Pat. Nos. 3,876,523 and 4,016,067. U.S. Pat. Nos. 3,891,541 and 3,931,052 disclose the demetalation and desulfurization of petroleum oils through the use of a conventional HDT catalyst whose pores are substantially distributed over a narrow 180 to 300 Angstrom diameter range.
Metals and sulfur contaminants are removed from residual oil fractions by catalytic contact with a series of catalysts in U.S. Pat. Nos. 4,016,067 and 4,054,508. In the processes of these patents, advantage is taken of different pore size distributions for the separate functions of demetalation and desulfurization.
U.S. Pat. Nos. 3,716,479 and 3,772,185 propose demetalation of a charge stock by contact with added hydrogen in the presence of a catalyst material derived from a manganese nodule.
Demetalation of hydrocarbon fractions is taught in U.S. Pat. No. 2,902,429 as contacting said fractions with a catalyst having a relatively small amount of sulfur-resistant hydrogenation-dehydrogenation component disposed on a low surface area carrier. Examples of such low surface area carriers include diatomaceous earth, natural clays and Alundum.
U.S. Pat. No. 3,867,282 describes a process for oil demetalation and desulfurization using a catalyst comprising a cobalt-molybdenum impregnated magnesium aluminate spinel.
Regeneration of catalysts used in residual oil hydroprocessing has been generally limited to hydrodesulfurization catalysts, as is illustrated by U.S. Pat. No. 3,565,820. Conventional hydrotreating catalysts can tolerate only 6 to 7% metals (Ni and V) and are not regenerable, thus it would be very desirable to have an effective regenerable catalyst for demetalation.
Regeneration of catalysts is preferred over the use of throw-away catalysts. Throw-away catalysts present disposal problems as well as relatively low activity. Also the use of regenerable catalysts would tend to be less expensive in the long run than throw-away catalysts. The use of metal tolerant, regenerable catalysts will not only decrease process costs, but more importantly will enhance the economic feasibility of treating high metal resids and heavy oils.
It is generally known in the art that leaching alkali silicate glasses with acids results in porous absorbents which are reported to exhibit molecular sieve-type absorption toward small molecules. In general, the glasses consist of three components: an alkali such as sodium or potassium, another oxide such as B.sub.2 O.sub.3 or Al.sub.2 O.sub.3, and silica. Porous glass with uniform pore sizes of 3 to 10 Angstroms has been reported. The porosity of said glasses is produced by acid leaching and the pore size distribution is controlled by the degree of acid leaching.
A novel catalyst composition comprising the oxides or sulfides of a Group VI metal and a Group VIII metal deposited within a porous glass support of controlled pore size is disclosed in U.S. Patent application Ser. No. 083,022 (filed Oct. 9, 1979) now abandoned for Ser. No. 250,808 (filed Apr. 3, 1981). The process of the instant invention employs this novel catalyst in processes for the catalytic demetalation and desulfurization of oil.
An objective of this invention is to provide means for the removal of metal and sulfur contaminants from oils. A further objective of this invention is to provide means for removal of metal and sulfur contaminants from residual hydrocarbon fractions. Another objective of this invention is to provide a method whereby hydrocarbon fractions having a significant metal and sulfur content may be demetalized and desulfurized in order to produce a suitable charge stock for cracking, hydrocracking or coking.